/*
 * QEMU BOOTP/DHCP server
 *
 * Copyright (c) 2004 Fabrice Bellard
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
#include <slirp.h>

/* XXX: only DHCP is supported */

#define LEASE_TIME (24 * 3600)

static const uint8_t rfc1533_cookie[] =
{ RFC1533_COOKIE};

#ifdef DEBUG
#define dprintf(fmt, ...) \
do if (slirp_debug & DBG_CALL) { fprintf(dfd, fmt, ##  __VA_ARGS__); fflush(dfd); } while (0)
#else
#define dprintf(fmt, ...)
#endif

// Get a IP address for a given mac address.
// At most 16 address is in the pool, select one from the pool and return it to the client.
static BOOTPClient *get_new_addr(Slirp *slirp, struct in_addr *paddr,
		const uint8_t *macaddr)
{
	BOOTPClient *bc;
	int i;

	// TODO: things can be done here.
	for (i = 0; i < NB_BOOTP_CLIENTS; i++)
	{
		bc = &slirp->bootp_clients[i];
		if (!bc->allocated || !memcmp(macaddr, bc->macaddr, 6))
			goto found;
	}
	return NULL;
	found: bc = &slirp->bootp_clients[i];
	bc->allocated = 1;
	paddr->s_addr = slirp->vdhcp_startaddr.s_addr + htonl(i);
	return bc;
}

// request for IP: paddr. Try to get longer release for this address.
static BOOTPClient *request_addr(Slirp *slirp, const struct in_addr *paddr,
		const uint8_t *macaddr)
{
	uint32_t req_addr = ntohl(paddr->s_addr);
	uint32_t dhcp_addr = ntohl(slirp->vdhcp_startaddr.s_addr);
	BOOTPClient *bc;

	// Supply at most 16 IP addresses, addresses out of this range will be ignored.
	if (req_addr >= dhcp_addr && req_addr < (dhcp_addr + NB_BOOTP_CLIENTS))
	{
		bc = &slirp->bootp_clients[req_addr - dhcp_addr];
		// If this IP is not allocated for other hosts and the mac address match,
		// then allocate it again with longer release.
		if (!bc->allocated || !memcmp(macaddr, bc->macaddr, 6))
		{
			bc->allocated = 1;
			return bc;
		}
	}
	return NULL;
}

// Find if mac address "macaddr" has got an IP address.
static BOOTPClient *find_addr(Slirp *slirp, struct in_addr *paddr,
		const uint8_t *macaddr)
{
	BOOTPClient *bc;
	int i;

	for (i = 0; i < NB_BOOTP_CLIENTS; i++)
	{
		if (!memcmp(macaddr, slirp->bootp_clients[i].macaddr, 6))
			goto found;
	}
	return NULL;
	found: bc = &slirp->bootp_clients[i];
	bc->allocated = 1;
	paddr->s_addr = slirp->vdhcp_startaddr.s_addr + htonl(i);
	return bc;
}

// Decode DHCP requests into certain data structures.
static void dhcp_decode(const struct bootp_t *bp, int *pmsg_type,
		const struct in_addr **preq_addr)
{
	const uint8_t *p, *p_end;
	int len, tag;

	*pmsg_type = 0;
	*preq_addr = NULL;

	p = bp->bp_vend;
	p_end = p + DHCP_OPT_LEN;
	if (memcmp(p, rfc1533_cookie, 4) != 0)
		return;
	p += 4;
	while (p < p_end)
	{
		tag = p[0];
		if (tag == RFC1533_PAD)
		{
			p++;
		}
		else if (tag == RFC1533_END)
		{
			break;
		}
		else
		{
			p++;
			if (p >= p_end)
				break;
			len = *p++;
			dprintf("dhcp: tag=%d len=%d\n", tag, len);

			switch (tag)
			{
			case RFC2132_MSG_TYPE:
				if (len >= 1)
					*pmsg_type = p[0];
				break;
			case RFC2132_REQ_ADDR:
				if (len >= 4)
					*preq_addr = (struct in_addr *) p;
				break;
			default:
				break;
			}
			p += len;
		}
	}
	if (*pmsg_type == DHCPREQUEST && !*preq_addr && bp->bp_ciaddr.s_addr)
	{
		*preq_addr = &bp->bp_ciaddr;
	}
}

// Generate a reply packet and send it to the client.
static void bootp_reply(Slirp *slirp, const struct bootp_t *bp)
{
	BOOTPClient *bc = NULL;
	struct mbuf *m;
	struct bootp_t *rbp;
	struct sockaddr_in saddr, daddr;
	const struct in_addr *preq_addr;
	int dhcp_msg_type, val;
	uint8_t *q;

	/* extract exact DHCP msg type */
	dhcp_decode(bp, &dhcp_msg_type, &preq_addr);

	dprintf("bootp packet op=%d msgtype=%d", bp->bp_op, dhcp_msg_type);
	if (preq_addr)
		dprintf(" req_addr=%08x\n", ntohl(preq_addr->s_addr));
	else
		dprintf("\n");

	if (dhcp_msg_type == 0)
		dhcp_msg_type = DHCPREQUEST; /* Force reply for old BOOTP clients */

	// If the dhcp message is neither DHCPDISCOVERY nor DHCPREQUEST, then nothing need to
	// be done.
	if (dhcp_msg_type != DHCPDISCOVER && dhcp_msg_type != DHCPREQUEST)
		return;
	/* XXX: this is a hack to get the client mac address */
	memcpy(slirp->client_ethaddr, bp->bp_hwaddr, 6);

	// Get a free space for DHCP Reply Packet.
	m = m_get(slirp);
	if (!m)
	{
		return;
	}

	// Skip the Ethernet header.
	m->m_data += IF_MAXLINKHDR;
	// Get the address for bootp.
	rbp = (struct bootp_t *) m->m_data;
	// Skip the UDP header.
	m->m_data += sizeof(struct udpiphdr);
	// Reset the whole reply packet.
	memset(rbp, 0, sizeof(struct bootp_t));

	if (dhcp_msg_type == DHCPDISCOVER)
	{
		// If an IP address is given in the request packet, then try to request for longer
		// release.
		if (preq_addr)
		{
			// Check if the given IP address is available.
			bc = request_addr(slirp, preq_addr, slirp->client_ethaddr);
			if (bc)
			{
				daddr.sin_addr = *preq_addr;
			}
		}

		// If no corresponding record exists in the cache.
		if (!bc)
		{
			// Try to get an IP address for the given mac address from the DHCP pool.
			new_addr: bc = get_new_addr(slirp, &daddr.sin_addr,
					slirp->client_ethaddr);

			// Unfortunately, no address is available.
			if (!bc)
			{
				dprintf("no address left\n");
				return;
			}
		}
		memcpy(bc->macaddr, slirp->client_ethaddr, 6);
	}
	// The packet is a DHCPREQUEST and an requested IP is given.
	else if (preq_addr)
	{
		// Request for the given IP address.
		bc = request_addr(slirp, preq_addr, slirp->client_ethaddr);
		if (bc)
		{
			// If the IP is available.
			daddr.sin_addr = *preq_addr;
			memcpy(bc->macaddr, slirp->client_ethaddr, 6);
		}
		else
		{
			daddr.sin_addr.s_addr = 0;
		}
	}
	else
	{
		bc = find_addr(slirp, &daddr.sin_addr, bp->bp_hwaddr);
		if (!bc)
		{
			/* if never assigned, behaves as if it was already
			 assigned (windows fix because it remembers its address) */
			goto new_addr;
		}
	}

	saddr.sin_addr = slirp->vhost_addr;
	saddr.sin_port = htons(BOOTP_SERVER);

	daddr.sin_port = htons(BOOTP_CLIENT);

	rbp->bp_op = BOOTP_REPLY;
	rbp->bp_xid = bp->bp_xid;
	rbp->bp_htype = 1;
	rbp->bp_hlen = 6;
	memcpy(rbp->bp_hwaddr, bp->bp_hwaddr, 6);

	rbp->bp_yiaddr = daddr.sin_addr; /* Client IP address */
	rbp->bp_siaddr = saddr.sin_addr; /* Server IP address */

	q = rbp->bp_vend;
	memcpy(q, rfc1533_cookie, 4);
	q += 4;

	// If an IP address is allocated for the request.
	if (bc)
	{
		dprintf("%s addr=%08x\n",
				(dhcp_msg_type == DHCPDISCOVER) ? "offered" : "ack'ed",
				ntohl(daddr.sin_addr.s_addr));

		if (dhcp_msg_type == DHCPDISCOVER)
		{
			*q++ = RFC2132_MSG_TYPE;
			*q++ = 1;
			*q++ = DHCPOFFER;
		}
		else /* DHCPREQUEST */
		{
			*q++ = RFC2132_MSG_TYPE;
			*q++ = 1;
			*q++ = DHCPACK;
		}

		if (slirp->bootp_filename)
			snprintf((char *) rbp->bp_file, sizeof(rbp->bp_file), "%s",
					slirp->bootp_filename);

		*q++ = RFC2132_SRV_ID;
		*q++ = 4;
		memcpy(q, &saddr.sin_addr, 4);
		q += 4;

		*q++ = RFC1533_NETMASK;
		*q++ = 4;
		memcpy(q, &slirp->vnetwork_mask, 4);
		q += 4;

		if (!slirp->restricted)
		{
			*q++ = RFC1533_GATEWAY;
			*q++ = 4;
			memcpy(q, &saddr.sin_addr, 4);
			q += 4;

			*q++ = RFC1533_DNS;
			*q++ = 4;
			memcpy(q, &slirp->vnameserver_addr, 4);
			q += 4;
		}

		*q++ = RFC2132_LEASE_TIME;
		*q++ = 4;
		val = htonl(LEASE_TIME);
		memcpy(q, &val, 4);
		q += 4;

		if (*slirp->client_hostname)
		{
			val = strlen(slirp->client_hostname);
			*q++ = RFC1533_HOSTNAME;
			*q++ = val;
			memcpy(q, slirp->client_hostname, val);
			q += val;
		}
	}
	// If no IP address is allocated (no address is available).
	else
	{
		static const char nak_msg[] = "requested address not available";

		dprintf("nak'ed addr=%08x\n", ntohl(preq_addr->s_addr));

		*q++ = RFC2132_MSG_TYPE;
		*q++ = 1;
		*q++ = DHCPNAK;

		*q++ = RFC2132_MESSAGE;
		*q++ = sizeof(nak_msg) - 1;
		memcpy(q, nak_msg, sizeof(nak_msg) - 1);
		q += sizeof(nak_msg) - 1;
	}
	*q++ = RFC1533_END;

	daddr.sin_addr.s_addr = 0xffffffffu;

	m->m_len = sizeof(struct bootp_t) - sizeof(struct ip)
			- sizeof(struct udphdr);

	// Send the reply to the client.
	udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
}

void bootp_input(struct mbuf *m)
{
	struct bootp_t *bp = mtod(m, struct bootp_t *);

	if (bp->bp_op == BOOTP_REQUEST)
	{
		bootp_reply(m->slirp, bp);
	}
}
